We will complete work on defining action of FSH on mouse ovaries. We plan to study the interaction of estrogens with DNA of Leydig cells in strains of mice with high and low incidence of Leydig cell tumors, and to determine the distinctive enzymes induced which lead to DNA synthesis in susceptible strains as distinguished from resistant strains. We also plan to relate these to changes during the later period of induction wehn the final premalignant changes have occurred.